Parasites of the CNS Flashcards
You are presented with a horse that is:
- Stumbling and falling over the past week
- Is unsteady in its hindlimbs
- Has slight wear on the dorsum of its toes on the hindlimbs, so dragging its feet
- has left-sided gluteal muscle atrophy
- was able to be pulled to the left on the tail-pull test
- No cranial nerve deficits
Most common Presentation are the 3A’s: Asymmetric, Ataxic and focal muscle Atrophy
You suspect a parasitic infection, what is the possible etiology?
Sarcocystis neurona = equine protozoal myeloencephalitis (EPM)
This is an apicomplexa parasite
How can you confirm the presence of Sarcocystis neurona?
1) Immunoblot analysis
- S. neurona antibodies in serum and CSF
CSF: Sn and Sp of 89%
Serum: Sn of 89% and Sp of 71%
2) ELISA: Highly specific for S.neurona specific antibodies
note: You cannot do a PCR, its sensitivity is very low as Merozoites are not found in the CSF, and any free parasite DNA floating around is rapidly destroyed
3) PM: Acute hemorrhagic lesions and necrosis in the spinal cord
What is the Final Host to S. neurona ?
Opossum
What are the Intermediate hosts to S. neurona ?
- Domestic Cat
- Several wildlife species including raccoons, skunks, armadillo
What is the Aberrant (“dead-end”) host to S. neurona ?
- Horse
Where does Schizogony occur in the horse?
Muscle tissue, producing merozoites
Merozoites penetrate and infect neural tissue
What is treatment for S. neurona in horses?
- Ideal drug: Ponazuril: Antiprotozoal Oral Paste, 5mg/kg/day ~28 days
- Sulfonamides: Sulfadiazine orally, 20mg/kg
- Diclazuril and Toltrazuril: coccidiostat that kills parasites in early stages, used as a prophylactic
- NSAIDs
- Vitamin E
Caution: steroids are contraindicated in this case
How can S. neurona infection be prevented?
- Prevention is best
- Keep feed rooms and containers closed and sealed
- Prevent wildlife from getting into feed room
- Discard dropped grain to discourage birds/ scavengers
What is the Definitive/ Final Host of Neospora. caninum ?
- Dogs (incl dingo, coyotes and wolves)
NOT foxes! Cant blame them
What is the Intermediate host of Neospora caninum ?
- Mammals and birds
- Cattle being the main issue
Why is Neospora caninum important in cattle?
- Highly prevalent
- Causes 10-45% of abortions
How do dogs or other wild canids get Neospora caninum ?
- Eating tissue cyst infected meat/ placental tissue = exogenous transmission
- transmission via placenta or milk to puppies (usually the litter is all affected)
How do cattle get Neospora. caninum ?
- Eating infected food (silage or pasture) with oocysts = exogenous transmission
- Vertical transmission from cow to calf = endogenous transmission
Is Neospora. caninum transmissible to humans? (i.e. zoonotic)
No
How does Neospora. caninum affect the cow fetus?
- Multiplying tachyzoites cause cell necrosis in the fetal macrophages, neutrophils, spinal fluid, and other neural cells
How does Neospora. caninum affect the adult/ mature cow?
- Little or no pathology, unless immunocompromised
What will happen to a cow fetus if infected with Neospora. caninum early in gestation?
- Abortion
What will happen to a cow fetus if infected with Neospora. caninum mid to late gestation?
- Variety of congenital defects including neurological signs, myocarditis, ataxia, exopthalmia
- Can be born normal and be a persistent shedder
- Can be born normal and uninfected
Clinical signs will vary according to:
- Quantity and duration of parasitemia
- Effectiveness of maternal immune response
- Ability of fetus to mount an immune response
What usually has to happen in order for a dog to present with clinical signs of Neospora caninum?
Immunosuppression
Therefore presentation is as follow:
- Presents in puppies due to weak immune system
- Presents in dogs concurrently infected with Canine distemper or Ehrlichiosis
- Presents in older dogs with waning immune systems or treatment with steroids
What are the clinical signs associated with Neospora caninum in a YOUNG dog?
- Encephalomyelitis: hyperexcitability, depression, paresis/ paralysis, head tilt, seizures
- Myositis-polyradiculoneuritis: progressive pelvic limb paresis (bilateral, non-painful, rigid pelvic limbs)
How can Neospora caninum be diagnosed in a young dog showing neurological clinical signs?
- Clinical signs are a big indicator, especially if multiple littermates are showing signs
- IgG titer in serum
- Presence of antibodies in CSF
- Positive response to appropriate treatment
What is the treatment for Neospora. caninum in dogs?
- No perfect drug or combination available
Can try:
- Trimethoprim sulfadiazine + Pyrimethamine
- Trimethoprim sulfadiazine + Clindamycin
- Clindamycin
What is the treatment for Neospora. caninum in cattle?
- No effective treatment
- Culling of seropositive stock in the breeding herd
What is the Intermediate host of Toxoplasma. gondii?
- Sheep
- Humans
- (Warm-blooded animals)
- NOT common in cattle or horses
